U.S. patent number 10,375,635 [Application Number 16/173,540] was granted by the patent office on 2019-08-06 for method and apparatus for transmission management in a wireless communication system.
This patent grant is currently assigned to InterDigital Technology Corporation. The grantee listed for this patent is InterDigital Technology Corporation. Invention is credited to Sudheer A. Grandhi, Robert L. Olesen, Mohammed Sammour.
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United States Patent |
10,375,635 |
Sammour , et al. |
August 6, 2019 |
**Please see images for:
( Certificate of Correction ) ** |
Method and apparatus for transmission management in a wireless
communication system
Abstract
A method and apparatus may be used in wireless communications.
The apparatus may be an access point (AP), and may transmit a power
save frame. The power save frame may include one or more Uplink
(UL) Transmission Times (ULT)s. The apparatus may determine that a
station (STA) did not transmit during its respective ULT. The AP
may transmit another power save frame. The other power save frame
may include a modified ULT. The modified ULT may be for a STA that
did not transmit during its respective ULT. The other power save
frame may include an unmodified ULT. The unmodified ULT may be for
a STA that did not transmit.
Inventors: |
Sammour; Mohammed
(Alrabieh-Amman, JO), Grandhi; Sudheer A.
(Pleasanton, CA), Olesen; Robert L. (Huntington, NY) |
Applicant: |
Name |
City |
State |
Country |
Type |
InterDigital Technology Corporation |
Wilmington |
DE |
US |
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Assignee: |
InterDigital Technology
Corporation (Wilmington, DE)
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Family
ID: |
37685982 |
Appl.
No.: |
16/173,540 |
Filed: |
October 29, 2018 |
Prior Publication Data
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Document
Identifier |
Publication Date |
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US 20190069237 A1 |
Feb 28, 2019 |
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Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
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15583435 |
May 1, 2017 |
10117179 |
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14135758 |
Jun 13, 2017 |
9681377 |
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11533072 |
Dec 31, 2013 |
8619658 |
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60719035 |
Sep 21, 2005 |
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60720967 |
Sep 27, 2005 |
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60736255 |
Nov 14, 2005 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
H04W
72/042 (20130101); H04W 72/0413 (20130101); H04W
52/0219 (20130101); H04J 3/0605 (20130101); H04W
74/04 (20130101); H04W 72/005 (20130101); H04W
72/14 (20130101); H04W 52/0216 (20130101); Y02D
30/70 (20200801); Y02D 70/22 (20180101); H04W
74/06 (20130101); H04L 43/10 (20130101); Y02D
70/142 (20180101) |
Current International
Class: |
H04J
3/06 (20060101); H04W 72/00 (20090101); H04W
72/04 (20090101); H04W 72/14 (20090101); H04W
52/02 (20090101); H04L 12/26 (20060101); H04W
74/04 (20090101); H04W 74/06 (20090101) |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1501646 |
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Jun 2004 |
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CN |
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11-69431 |
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Mar 1999 |
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JP |
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10-2002-0095251 |
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Dec 2002 |
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KR |
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2004-0072815 |
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Aug 2004 |
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KR |
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2004-0104776 |
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Dec 2004 |
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KR |
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10-2006-0090258 |
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Aug 2006 |
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KR |
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I436673 |
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May 2014 |
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TW |
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2005/039127 |
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Apr 2005 |
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WO |
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Other References
IEEE, "Draft Amendment to Standard [for] Information Technology
Telecommunications and Information Exchange between Systems-Local
and Metropolitan Networks-Specific Requirements-Part 11: Wireless
LAN Medium Access Control (MAC) and Physical Layer (PHY)
Specifications: Enhancements for Higher Throughput", IEEE
P802.11n.TM./D0.01, Jan. 2006, 191 pages. cited by applicant .
IEEE, "Draft Amendment to Standard for Information
Technology-Telecommunications and Information Exchange Between
Systems-Local and Metropolitan Area Networks-Specific
Requirements-Part 11: Wireless LAN Medium Access Control (MAC) and
Physical Layer (PHY) Specifications; Amendment: Enhancements for
Higher Throughput", IEEE 802.11n/D1.02, Jul. 2006. cited by
applicant .
IEEE, "IEEE Wireless LAN Edition-A Compilation Based on IEEE Std
802.11 TM-1999 (R2003) and Its Amendments", 2003, pp. 1-705. cited
by applicant .
IEEE, "Telecommunications and Information Exchange Between
Systems-Local and Metropolitan Area Networks-Specific Requirements,
Part 11: Wireless Medium Access Control (MAC) and Physical Layer
(PHY) Specifications: Amendment 7: Medium Access Control (MAC)
Quality of Services (QoS) Enhancements", IEEE P802.11e/D9.0, Aug.
2004. cited by applicant .
IEEE, "Telecommunications and Information Exchange Between
Systems-Local and Metropolitan Area Networks-Specific Requirements,
Part 11: Wireless LAN Medium Access Control (MAC) and Physical
Layer (PHY) Specifications; Amendment 4: Further Higher Data Rate
Extension in the 2.4 Ghz Band", Jun. 27, 2003. cited by applicant
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Jang et al., "Samsung MAC Proposal Technical Specification", IEEE
802.11-04-0918-00-000n, Aug. 2004. cited by applicant .
Kose et al., "\MNiSE Proposal: High Throughput Extension to the
802.11 Standard", IEEE 802.11-05/0149r5, Mar. 18, 2005, 1OS pages.
cited by applicant .
Kose et al., "\MNiSE Proposal: High Throughput Extension to the
802.11 Standard", IEEE 802.11-05/0149r1, Jan. 6, 2005. cited by
applicant .
Mujtaba et al., "TGn Sync Proposal Technical Specification", IEEE
802.11-04/0889r6, May 18, 2005, 131 pages. cited by applicant .
Mujtaba et al., "TGn Sync Proposal Technical Specification", IEEE
802.11-04/0889r5, May 13, 2005, 131 pages. cited by applicant .
Mujtaba, Syed Aon, "TGn Sync Proposal Technical Specification",
IEEE 802.11-04/0889r2, IEEE P802.11 Wireless LANs, Jan. 2005, 152
pages. cited by applicant .
Mujtaba, Syed Aon, "TGn Sync Proposal Technical Specification",
IEEE 802.11-04/0889r7, Jul. 8, 2005, 7 pages. cited by
applicant.
|
Primary Examiner: Miller; Brandon J
Attorney, Agent or Firm: Volpe and Koenig, P.C.
Parent Case Text
CROSS REFERENCE TO RELATED APPLICATIONS
This application is a continuation of U.S. patent application Ser.
No. 15/583,435, filed May 1, 2017, which is a continuation of U.S.
patent application Ser. No. 14/135,758 filed Dec. 20, 2013, which
issued as U.S. Pat. No. 9,681,377 on Jun. 13, 2017, which is a
continuation of U.S. patent application Ser. No. 11/533,072 filed
Sep. 19, 2006, which issued as U.S. Pat. No. 8,619,658 on Dec. 31,
2013, which claims the benefit of U.S. Provisional Application No.
60/719,035, filed Sep. 21, 2005, U.S. Provisional Application No.
60/720,967, filed Sep. 27, 2005, and U.S. Provisional Application
No. 60/736,255, filed Nov. 14, 2005, the contents of which are
hereby incorporated by reference.
Claims
What is claimed is:
1. An IEEE 802.11 station (STA) comprising: a transceiver
configured to receive, from an access point (AP), a first frame
that includes a first uplink transmission time (ULT) associated
with the STA during which the STA is permitted to transmit uplink
data to the AP; a processor, coupled to the transceiver, configured
to determine whether a wireless medium is available, and to
transmit, along with the transceiver, uplink data to the AP when it
is determined that the wireless medium is available, wherein on a
condition that the processor and transmitter do not transmit uplink
data during the first ULT associated with the STA, the processor
and transceiver are configured to receive a second frame during the
first ULT that includes a modified ULT associated the STA during
which the STA is permitted to transmit uplink data to the AP; and
the processor and the transceiver configured to transmit uplink
data to the AP during the modified ULT associated with the STA.
2. The STA of claim 1, wherein the first frame is a power save
frame.
3. The STA of claim 1, wherein the first and second power save
frames are multiple receiver aggregate multi-poll/power save
aggregation descriptor (MMP/PSAD) frames.
4. The STA of claim 1, wherein the first frame includes a second
uplink transmission time (ULT) associated with a second station
(STA).
5. The STA of claim 4, wherein the second frame includes the second
ULT associated with the second STA.
6. The STA of claim 5, wherein the second ULT received in the
second frame is unchanged as compared to the second ULT received in
the first frame.
7. The STA of claim 1, wherein the processor and the transceiver
are configured to receive the second frame after a point control
function inter-frame spacing (PIFS) period after the start of the
first ULT.
8. A method for use in an IEEE 802.11 station (STA), the method
comprising: receiving, from an access point (AP), a first frame
that includes a first uplink transmission time (ULT) associated
with the STA during which the STA is permitted to transmit uplink
data to the AP; determining whether a wireless medium is available;
transmitting uplink data to the AP when it is determined that the
wireless medium is available; on a condition that it is determined
that the wireless medium is not available during the first ULT, not
transmitting uplink data during the first ULT associated with the
STA, and receiving a second frame during the first ULT that
includes a modified ULT associated the STA during which the STA is
permitted to transmit uplink data to the AP; and transmitting
uplink data to the AP during the modified ULT associated with the
STA.
9. The method of claim 8, wherein the first frame is a power save
frame.
10. The method of claim 8, wherein the first and second power save
frames are multiple receiver aggregate multi-poll/power save
aggregation descriptor (MMP/PSAD) frames.
11. The method of claim 8, wherein the first frame includes a
second uplink transmission time (ULT) associated with a second
station (STA).
12. The method of claim 11, wherein the second frame includes the
second ULT associated with the second STA.
13. The method of claim 12, wherein the second ULT received in the
second frame is unchanged as compared to the second ULT received in
the first frame.
14. The method of claim 8, further comprising: receiving the second
frame after a point control function inter-frame spacing (PIFS)
period after the start of the first ULT.
Description
FIELD OF INVENTION
The present invention is related data transmission in a wireless
communication system. In particular, the present invention relates
to a method and apparatus for transmission management for multiple
polling and power saving in a wireless communication system.
BACKGROUND
The implementation of proposed IEEE 802.11 standards, and in
particular the IEEE 802.11n standard, will allow for higher
throughput (HT) wireless local area network (WLAN) devices. One
such way in which higher throughput may be achieved is through the
use of signal aggregation in both the medium access control (MAC)
layer and the physical (PHY) layer. When an aggregate is addressed
to a single receiver address, it is referred to as a Single
Receiver Aggregate (SRA). When the aggregate is addressed to
multiple receivers, it is referred to as a Multiple Receiver
Aggregate (MRA).
An MRA may be transmitted during a Multiple Receiver Aggregate
Multi-Poll (MMP) sequence or a Power Save Aggregation Descriptor
(PSAD). This aggregation tends to improve system performance and
also provides a power saving mechanism in the case of MMP/PSAD.
One or more MAC Service Data Units (MSDUs) being sent to the same
receiver can be aggregated into a single Aggregate-MSDU (A-MSDU).
This aggregation of more than one frame improves the efficiency of
the MAC layer, particularly when there are many small MSDUs such as
Transmission Control Protocol Acknowledgements (TCP ACKs). The
overhead associated with channel access, such as the Physical Layer
Convergence Protocol (PLCP) preamble, MAC header, and IFS spacing,
can thereby be amortized over two or more MSDUs. Additionally, a
STA may only use MSDU aggregation where it knows that the receiver
supports MSDU aggregation. In some cases, support for MSDU
aggregation may be mandatory at the receiver.
FIG. 1 shows an exemplary A-MSDU frame 10. The A-MSDU frame 10
includes a plurality of Sub-frame header fields 11 and a plurality
of MSDU fields 12 (designated MSDU.sub.1 . . . MSDU.sub.n). Each
Sub-frame header field 11 includes an MSDU length field 13, a
source address (Source Addr) field 14, and a destination address
(Dest Addr) field 15. Typically, the sub-frame header fields 11
separate the MSDU to aid a receiver in deciphering whether or not
the frame is directed toward it. Ordinarily, the MSDU length field
13 includes the length, the Source Addr field 14 includes the
address of the transmitter, and the Dest Addr field 15 includes the
address of the receiver. In general, to form an A-MSDU 10, two or
more MSDUs are aggregated together.
Another type of aggregation may be formed by joining multiple MAC
Protocol Data Units (MPDUs) together. FIG. 2 shows an exemplary
aggregated MPDU (A-MPDU) frame 20. The A-MPDU frame 20 includes a
plurality of MPDU delimiter fields 21 and a plurality of MPDU
fields 22 (designated MPDU.sub.1 . . . MPDU.sub.n). Each MPDU
delimiter field 21 also includes a reserved field 31, an MSDU
length field 24, a Cyclic Redundancy Check (CRC) field 25, and a
Unique Pattern field 26. The A-MPDU frame 20 is typically
transported in a single aggregate PLCP Service Data Unit (A-PSDU).
Additionally, padding octets (not shown) are appended, if needed,
to make each MPDU field 22 section a multiple of four octets in
length, except in the case of MPDU.sub.n.
One purpose of the MPDU delimiter field 21 is to delimit the MPDUs
22 within the aggregate. For example, the structure of the
aggregate can usually be recovered when one or more MPDU delimiters
are received with errors. Also, individual MPDU delimiter fields 21
have the same block error rate (BER) as the surrounding MPDUs 22,
and can therefore be lost during transmission.
One advantage in using A-MPDU frames 20 is that, unlike A-MSDUs,
they can be aggregated to multiple receivers. That is, a
multiple-receiver aggregate (MRA) may contain MPDUs that are
addressed to multiple receivers. Moreover, an MRA may be
transmitted in one of two contexts that are distinguished by
whether it is transmitted during an MMP/PSAD sequence or not. If
multiple responses are required, they may be scheduled by
transmission of an MMP or PSAD frame.
FIG. 3 shows a typical multiple receiver aggregate multi-poll (MMP)
frame 30. The MMP frame 30 includes a frame control field 31, a
duration field 32, a receiver address (RA) field 33, a transmitter
address (TA) field 34, a number of receivers (N) field 35, a
receiver information (info) field 36, and a frame checksequence
(FCS) field 37. The RA field 33 is typically the broadcast address
of a group. The TA field 34 is typically the address of the
wireless transmit/receive unit (WTRU) transmitting the MRA
aggregate. The number of receivers (N) field 35 includes the number
of receivers for which MPDUs are included in the MRA aggregate.
Additionally, the receiver info field 36 includes a plurality of
subfields, such as an association identifier (AID) field 61, a
transmission identifier (TID) field 62, a new PPDU flag field 63, a
reserved field 64, a receive (Rx) offset field 65, an Rx duration
field 66, a transmit (Tx) offset field 67, and a Tx duration field
68. The AID field 61 identifies a station (STA) addressed by the
frame. The TID field 62 defines the TID for transmissions by a STA.
The new PPDU flag field 63 indicates that the downlink (DL) for the
STA begins at the start of the PPDU. The Rx offset field 65 defines
the start of the first symbol containing DL data for a STA. The Rx
duration field 66 defines the length of a downlink. The Tx offset
field 67 defines the time when transmissions by the STA may begin,
and the Tx duration field 68 defines the duration limit of the
transmissions.
FIG. 4 shows a typical power save aggregation descriptor (PSAD)
frame 40. The PSAD frame 40 includes a frame control field 41, a
duration field 42, an RA field 43, a TA field 44, a basic service
set identifier (BSSID) field 45, a PSAD parameter (PARAM) field 46,
a number of receivers field 47, and an FCS field 48. The PSAD PARAM
field 46 further includes a reserved field 71, a More PSAD
indicator 72, and a descriptor end field 73. The number of
receivers field 47 includes a plurality of individual Station Info
fields which further includes a reserved field 81, a STA ID field
82, a downlink transmission (DLT) start offset field 83, a DLT
duration field 84, an uplink transmission (ULT) start offset field
85, and a ULT duration field 86.
An MMP/PSAD frame may be transmitted as a non-aggregate, or may be
aggregated with downlink MPDUs. Since the MMP/PSAD frame format
defines receiving and transmitting durations for each STA, it
enables STAs to save power since the STA can go into sleep mode
when it is not either receiving or transmitting. Also, since the
MMP sequence is protected using a network allocation vector (NAV)
and extended PHY protection (EPP), MMP provides a mechanism of
scheduling multiple transmission opportunities (TXOPs).
FIG. 5A shows an MMP/PSAD Downlink frame exchange sequence 50, and
FIG. 5B shows an MMP/PSAD Uplink frame exchange sequence 55. In
PSAD, a downlink transmission (DLT) and an uplink transmission
(ULT) period of time are described by the PSAD frame 40. Which
period of time is intended to be used for the transmission of
frames from/to the PSAD transmitter to one of the PSAD receivers is
also described in the PSAD frame 40.
In particular, FIGS. 5A and 5B show the start offsets for DLT1 to
DLTn, and ULT1 to ULTn. Similarly, in MMP, offsets are shown for a
series of downlink transmissions RX1 to RXn and uplink
transmissions TX1 to TXn.
Aggregation is also possible at the PHY-level layer for physical
layer (PHY) protocol data units (PPDUs). This aggregation may be
referred to as an aggregated PPDU (A-PPDU). An A-PPDU contains one
or more pairs of PLCP headers and PPDUs or PHY service data units
PSDUs. To form an A-PPDU, two or more PPDUs (or PSDUs) are
aggregated together, separated by the High Throughput Signal
(HT-SIG) field.
FIG. 6 shows a typical aggregated PPDU (A-PPDU) 60. The A-PPDU 60
includes a legacy preamble (L-Preamble) 91, a High-Throughput
Preamble (HT-Preamble) 92, a plurality of PSDU fields 93
(PSDU.sub.1 . . . PSDU.sub.n), and a plurality of HT-Signal
(HT-SIG) fields 94 (HT-SIG.sub.1 . . . HT-SIG.sub.n). An HT-SIG
field 94 may also include a length field 95, an MCS field 96, an
advanced coding field 97, a sounding packet 98, a number HT-Legacy
Training Field (HT-LTF) 99, a Short GI field 101, a 20/40 field
102, a cyclic redundancy check (CRC) field 103, and a tail field
104.
As shown in FIG. 6, the resulting A-PPDU 60 is therefore the
combination of all PPDUs (or PSDUs) in the A-PPDU along with
HT-SIGs 94 for each constituent PSDU 93. Since each PSDU 93 shown
in FIG. 6 is delimited by an HT-SIG 94 that defines the various
physical layers parameters, the A-PPDU comprises multi-rate
PSDUs.
One of the drawbacks to the current system, however, is that when
an MMP/PSAD is transmitted by the AP, it is possible that one or
more of the STAs associated with the MMP/PSAD will not correctly
receive, or incorrectly decode the MMP/PSAD frame. In these cases,
the STAs that do not correctly receive or decode the MMP/PSAD frame
will miss their scheduled uplink transmission times, effectively
wasting the WLAN medium time.
It would therefore be advantageous if a method and apparatus
existed that served as a mechanism to recover the structure of the
A-PPDU 90 if one or more HT-SIGs 94 or PSDUs 93 are received in
error due to poor channel conditions. It would further be
advantageous for a method and apparatus to exist wherein an AP
recovers any unused ULT, can transmit multiple MMP/PSAD frames, and
can schedule multicast and broadcast transmissions in MMP/PSAD
frames.
SUMMARY
In a wireless communication system comprising at least one access
point (AP) and a plurality of stations (STAs), a method for
transmission management of the wireless medium comprises the AP
configuring a Multiple Receiver Aggregate Multi-Poll/Power Save
Aggregation Descriptor (MMP/PSAD) frame with scheduled Uplink
Transmission Time (ULT) information for the plurality of STAs. The
AP then transmits the MMP/PSAD frame to the plurality of STAs. Upon
successfully receiving and decoding the MMP/PSAD frame, STAs
transmit during their scheduled ULT.
A method and apparatus may be used in wireless communications. The
apparatus may be an access point (AP), and may transmit a power
save frame. The power save frame may include one or more Uplink
(UL) Transmission Times (ULT)s. The apparatus may determine that a
station (STA) did not transmit during its respective ULT. The AP
may transmit another power save frame. The other power save frame
may include a modified ULT. The modified ULT may be for a STA that
did not transmit during its respective ULT. The other power save
frame may include an unmodified ULT. The unmodified ULT may be for
a STA that did not transmit.
A STA may receive a power save frame. The power save frame may
include one or more ULTs. One of the ULTs may be a scheduled ULT
for the STA. If the STA does not transmit during the scheduled ULT,
the STA may receive another power save frame. The other power save
frame may include a modified ULT for the STA. The STA may transmit
packet data based on the modified ULT. The other power save frame
may include an unmodified ULT for another STA.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing summary, as well as the following detailed
description of the preferred embodiments of the present invention
will be better understood when read with reference to the appended
drawings, wherein:
FIG. 1 shows an exemplary A-MSDU frame;
FIG. 2 shows an exemplary aggregated MPDU (A-MPDU) frame;
FIG. 3 shows a typical multiple receiver aggregate multi-poll (MMP)
frame;
FIG. 4 shows a typical power save aggregation descriptor (PSAD)
frame;
FIG. 5A shows an MMP/PSAD Downlink frame exchange sequence;
FIG. 5B shows an MMP/PSAD Uplink frame exchange sequence;
FIG. 6 shows a typical aggregated PPDU (A-PPDU);
FIG. 7 shows a wireless communication system configured in
accordance with the present invention;
FIG. 8 is a functional block diagram of an AP and a STA configured
to perform a method for transmission management, in accordance with
the present invention;
FIG. 9 is a flow diagram for managing transmission times in the
wireless communication system of FIG. 7, in accordance with an
embodiment of the present invention;
FIG. 10 is an exemplary signal diagram of a downlink and uplink
exchange for the wireless communication system of FIG. 7, in
accordance with an embodiment of the present invention;
FIG. 11 is an exemplary signal diagram of a downlink and uplink
exchange for the wireless communication system 100 where a
particular STA did not successfully receive and decode its downlink
and uplink scheduling information;
FIG. 12 is a flow diagram of a method of recovering the medium, in
accordance with an embodiment of the present invention;
FIG. 13 is an exemplary signal diagram of a downlink and uplink
exchange for the wireless communication system, showing a broadcast
or multicast MMP/PSAD transmitted during a broadcast phase of the
downlink phase; and
FIG. 14 is an exemplary signal diagram of a downlink and uplink
exchange for the wireless communication system, showing a broadcast
or multicast MMP/PSAD transmitted between the downlink and uplink
phases.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Hereafter, a station (STA) includes but is not limited to a
wireless transmit/receive unit (WTRU), user equipment (UE), mobile
station, fixed or mobile subscriber unit, pager, or any other type
of device capable of operating in a wireless environment. When
referred to hereafter, an access point (AP) includes but is not
limited to a base station, Node-B, site controller, access point or
any other type of interfacing device in a wireless environment.
FIG. 7 shows a wireless communication system 100 configured in
accordance with the present invention. The wireless communication
system 100 in a preferred embodiment may be a wireless local area
network (WLAN), and includes an AP 110 and a plurality of STAs 120
(designated STA1, STA2, and STA3) capable of wireless communication
with the AP 110. The AP 110, in a preferred embodiment, is
connected to a network 130, such as the Internet, a public switched
telephone network (PSTN), or the like. In this manner, the STAs 120
are provided access to the network 130 through the AP 110. Although
only three STAs 120 are depicted in the wireless communication
system 100, it should be noted that any number of STAs 120 may
exist in the wireless communication system 100 and be in
communication with the AP 110.
FIG. 8 is a functional block diagram of an AP 110 in communication
with a STA 120, configured to perform a method for transmission
management in the wireless system 100.
In addition to the components normally included in a typical AP,
the AP 110 includes a processor 115 configured to manage
transmission in the wireless communication network 100, a receiver
116 in communication with the processor 115, a transmitter 117 in
communication with the processor 115, and an antenna 118 in
communication with the receiver 116 and the transmitter 117 in
order to facilitate wireless transmission and reception.
Additionally, in a preferred embodiment, the processor 115 is
capable of communicating with the network 130.
In addition to the components normally included in a typical STA,
the STA 120 includes a processor 125 configured to manage
transmission in the wireless communication system 100, a receiver
126 in communication with the processor 125, a transmitter 127 in
communication with the processor 125, and an antenna 128 in
communication with the receiver 126 and the transmitter 127 in
order to facilitate wireless transmission and reception.
FIG. 9 is a flow diagram 900 for managing transmission times in the
wireless communication system 100, in accordance with an embodiment
of the present invention. In step 910, the AP 110 configures an
MMP/PSAD frame in order to signal to STAs 120 their transmit times
in the UL phase. Specifically, the MMP/PSAD frame schedules both
downlink and uplink frame exchanges for a subsequent duration of
time that is specified in the MMP/PSAD duration field. For example,
the AP 110 may achieve this by arranging the order of PSAD
descriptor fields (or the MMP Receiver Information fields)
according to increasing values of the Rx/DLT Start Offset, or
according to the order of transmission when the Rx/DLT Start Offset
is equal. This is particularly useful if the AP 110 is sending an
A-PPDU containing multiple PPDUs destined to multiple receiver STAs
120. Additionally, the AP 110 populates the TA field (34,44) with
its own identifier, such as its MAC address, and the RA field with
addresses of intended receivers. In one embodiment, the RA field
may be populated with the MAC addresses of the STAs 120 the
MMP/PSAD frame is intended for.
The AP 110 then transmits the MMP/PSAD frame to the STAs 120 (step
920). Each particular STA 120 then receives the MMP/PSAD frame
(step 930). If the particular STA 120 receives and decodes the
MMP/PSAD frame successfully (step 940), the STA 120 extracts it
transmit time from the MMP/PSAD frame (step 950). If the STA 120
does not successfully receive and decode the MMP/PSAD frame (step
940), then the AP 110 recovers the medium (step 970), which will be
described in more detail below.
In one example, the STA 120 extracts timing information of the
individual PPDUs that form the A-PPDU aggregate. A STA 120 that
receives an MMP/PSAD frame can derive its HT-SIG time information
from the Offset field and Duration field that are defined within
the MMP/PSAD frame. Specifically, the Rx (or DLT) Start Offset and
Duration fields are used for the purpose of extracting the HT-SIG
timing information of an A-PPDU, thereby improving the reliability
of the A-PPDU aggregation scheme. This may also allow a simple
receiver implementation.
For purposes of example, it may be assumed that one of the
aggregates within the MMP/PSAD exchange is an A-PPDU aggregate. For
a STA 120 identified in the MMP/PSAD frame as having downlink data
within the MMP/PSAD exchange, the immediately preceding station's
MMP/PSAD Rx Offset and Rx Duration fields may be used in order to
determine the starting time of its HT-SIG field. However, this
sharing of Rx Offset information occurs only if both stations have
the same Rx Offset. Otherwise, the Rx Offset of the particular STA
120 is used. Accordingly, by adding the Rx Offset and Rx Duration
of the prior station, the particular STA 120 can determine when its
PPDU HT-SIG will start.
Alternatively, the particular STA 120 can use multiple prior fields
of the MMP/PSAD frame instead of only one prior field, such as only
the information of the immediately prior station. This variation
may be useful, for example, when the Rx Duration fields are not
defined relative to a common Rx Offset, but rather in terms of the
actual duration of the data PPDU. In this case, the particular STA
120 may need to perform an overall addition on the all previous Rx
Duration fields.
In another alternative, a field or bit is added within the MMP/PSAD
descriptor fields or the MMP Receiver Information fields. This
field or bit differentiates whether the timing information is
related to the start of an MPDU within an A-MPDU aggregate, or a
PPDU within an A-PPDU aggregate. For example, this added field
could be used to indicate that the particular STA 120 should expect
to receive and decode an HT-SIG at this Rx Offset, a preamble
training field, or an MPDU delimiter field.
If the A-PPDU is transmitted without the MMP/PSAD, it should be
protected with a network allocation vector (NAV) setting or
spoofing since the irregular error probability and error
propagation can disrupt the power savings, medium access and NAV of
other STAs 120 in the system. For example, an A-PPDU from the AP
110 can be preceded by a clear to send (CTS)-to-self transmission
to provide NAV and/or EPP protection. An A-PPDU from a Non-AP STA
120 may be protected by an RTS/CTS exchange for NAV and EPP
protection.
Once the STA 120 extracts its timing information (step 950), it
then transmits during its transmit time in the UL phase (step
960).
FIG. 10 is an exemplary signal diagram 101 of a downlink and uplink
exchange for the wireless communication system 100, in accordance
with the method 900 described above. The AP 110 transmits the
MMP/PSAD frame that includes the downlink and uplink scheduling
information for STA1, STA2, and STA3. In the downlink phase, the AP
110 transmits the downlink information for STA1, STA2, and STA3 as
indicated by D1, D2, and D3. If each STA 120 successfully received
and decoded the MMP/PSAD frame, then each STA 120 (STA1, STA2, and
STA3) receives its downlink information during its scheduled time
as D1, D2, and D3, respectively. In the uplink phase, STA1
transmits during its scheduled uplink time (U1), STA2 transmits
during its scheduled uplink time (U2), and STA3 transmits during
its scheduled uplink time (U3). In this manner, each STA 120 knows
when it needs to be active in order to receive downlink data
associated with it or to transmit during its scheduled uplink time.
Accordingly, each STA 120 can power down during times that it knows
it is not scheduled to transmit or receive, thereby allowing it to
conserve its energy.
Since the scheduling of uplink and downlink frame exchanges is
scheduled in the MMP/PSAD frame, a STA 120 that does not
successfully receive and decode the MMP/PSAD frame (step 940) will
not be aware of its timing and may miss its transmission
opportunity in the UL. Without any mechanism to prevent or recover
this from happening, the medium time may be wasted. To prevent this
from occurring, the AP 110 should recover the medium (step
970).
FIG. 11 is an exemplary signal diagram 101' of a downlink and
uplink exchange for the wireless communication system 100 where a
particular STA 120 (in this case STA2) did not successfully receive
and decode its downlink and uplink scheduling information in step
940. Accordingly, STA2 does not transmit during its scheduled
uplink time (U2').
FIG. 12 is a flow diagram of a method of recovering the medium 970,
in accordance with an embodiment of the present invention. In step
980, the AP 110 monitors the medium to detect whether or not
particular STAs 120 are transmitting during their scheduled UL
time. The AP 110 may utilize the timing information in the MMP/PSAD
frame to determine when it should monitor the medium (step 980), or
it may continuously monitor the medium.
If the AP 110 detects that a STA 120 is not conducting its uplink
transmissions when scheduled, the AP 110 may reclaim the medium
(step 990).
Referring again to FIG. 11, the AP 110 will monitor the Uplink
Phase and detect that STA1 transmits its uplink data during its
scheduled uplink window (U1). The AP 110 will then detect that
STA2, for example, is not transmitting during its scheduled uplink
transmit window (U2'). After waiting an idle period, AP 110 will
reclaim the medium (step 990).
In a preferred embodiment, the idle period is a pre-determined
period that the AP 110 will wait to give a STA 120 an ample
opportunity to begin transmitting during its uplink time, before
the AP 110 reclaims the medium. As an example, the idle time period
may be equal to the point control function inter-frame spacing
(PIFS) period. The AP 110 may monitor the medium (step 980) during
the MMP/PSAD exchange period if the AP 110 is not transmitting, or
since the AP 110 may know the time periods in which each STA 120 is
to be transmitting in the uplink, the AP 110 may only monitor the
medium during those times.
Alternatively, the AP 110 may monitor the medium for frame errors
or collisions that are occurring during the uplink phase, and base
a decision as to reclaiming the medium on those observations.
Additionally, the AP 110 may decide to cancel the MMP/PSAD in order
to transmit or schedule data traffic that has a higher priority
than what the AP 110 has already accounted for. For example, the AP
110 may wish to improve Quality of Service (QoS) requirements for
particular traffic, or to schedule control traffic.
At any rate, once the AP 110 has decided to reclaim the medium in
step 990, there are several ways by which it may do so.
One way in which the AP 110 may reclaim the medium is by
rescheduling DLT or ULT transmissions (step 991). In a preferred
embodiment, the AP 110 accomplishes this by transmitting a frame to
indicate to all or selected STAs 120 that they should disregard the
previously sent MMP/PSAD frame (step 992). This frame may have a
number of formats.
For example, the frame transmitted in step 992 may be a newly
defined frame to reset or cancel the prior MMP schedule, or any
control, management or data frame that can be configured to
indicate to the STAs 120 to reset prior MMP/PSAD schedules.
In one preferred embodiment, however, the AP 110 retransmits
another MMP/PSAD frame. The MMP/PSAD frame may be the original
MMP/PSAD frame, but containing a field that specifies that the
previous scheduling information should be ignored by all, or
selected, STAs 120. Alternatively, the MMP/PSAD frame may be
identical to the previously sent MMP/PSAD frame, but with a defined
rule specifying that if a STA 120 receives an MMP/PSAD frame, it is
to disregard any scheduling information received from any prior
MMP/PSAD frame.
A NAV duration of the new MMP/PSAD, or any frame used to cancel or
reset the prior MMP/PSAD schedule, may be utilized to reset or
update the NAV at the receiving STAs 120. Another frame, such as a
CF-END frame could also be used to reset the NAV durations of the
STAs 120. Alternatively, the wireless communication system 100 may
be configured such that the duration of the most recent MMP/PSAD
frame supersedes any locally stored NAV durations at the STAs
120.
Another way in which the AP 110 may reclaim the medium is by
transmitting a poll frame to the STA 120 that is not transmitting
during its scheduled transmit time (step 993). The poll frame may
include a contention free poll (CF-Poll), a QoS Poll, another
MMP/PSAD frame, or the like. Alternatively, the AP 110 may transmit
the poll frame to a different STA 120 than the scheduled STA for
uplink transmission. The STA 120 that receives the poll frame will
then begin transmitting in response to the poll frame (step 994).
If the STA 120 has data to transmit, then it will transmit the
data. Otherwise it will transmit an acknowledgement frame, a QoS
Null, a Data Null, or another frame to indicate that it does not
have any data to transmit.
Yet another way the AP 110 may reclaim the medium is by
transmitting downlink data and, in a preferred embodiment, a
reverse direction grant (RDG) signal, as in step 995. For example,
the AP 110 may send downlink data to any STA 120 that it desires,
or the AP 110 may transmit any control or management frame during
this period. Upon receiving the downlink data and RDG signal, the
receiving STA transmits its uplink data for its time duration (step
996). Even if the AP 110 does not possess any downlink data to
transmit, it may still transmit a Data Null, QoS Null, or the like,
to indicate to the non-transmitting STA that it should begin
transmitting for its specified duration.
For example, referring back to FIG. 11, if the AP 110 detects that
the medium is idle for too long after STA1's uplink transmission
(U1) time, then AP 110 transmits downlink data and an RDG to STA2.
Upon receiving the downlink data and RDG, STA2 transmits its data
for its specified duration (U2').
If the STA 120 does not have data to transmit in the uplink, the
STA 120 should transmit a response frame to the AP 110 such as a
QoS Null frame, a Data Null frame, or the like, to indicate to the
AP 110 that the STA does not have data to transmit during its
allotted uplink time. The AP 110 can thereby reclaim the medium and
take some other remedial action to avoid wasting the medium, such
as polling another STA 120 to begin its transmission.
Another way that the AP 110 may reclaim the medium is by
transmitting a redundant MMP/PSAD frame (step 997). The redundant
MMP/PSAD frame may repeat some or all of the ULT information during
the time when a STA 120 misses its transmission window in the
uplink phase. This is particularly useful if more than one STA 120
did not receive or decode the MMP/PSAD frame successfully. The AP
110 may also decide to utilize a redundant MMP/PSAD frame if it
detects certain events occurring in the wireless communication
system 100 during a previous MMP/PSAD exchange sequence, or because
the AP 110 possesses particular knowledge about the ULT information
or number of STAs 120, that would make it appropriate to transmit a
redundant MMP/PSAD.
For example, the AP 110 may have detected in a previous MMP/PSAD
frame exchange that certain STAs 120 did not transmit their
information during their scheduled uplink times. In this case, the
AP 110 may determine that in the next MMP/PSAD exchange, it will
transmit a redundant MMP/PSAD frame to enhance the probability that
all STAs 120 will properly receive their scheduled ULTs.
Additionally, the AP 110 may know that there are a large number of
STAs 120 in the wireless communication system 100, and therefore,
the probability of any particular STA 120 failing to receive its
ULT information in the first MMP/PSAD is increased. Similarly, the
AP 110 may have knowledge relating to extensive ULTs scheduled for
the STAs 120 in the wireless communication system 100, meaning that
if one STA 120 failed to receive the first MMP/PSAD, a large amount
of wasted bandwidth can occur if that STA fails to transmit during
its scheduled ULT. In these scenarios, transmitting a redundant
MMP/PSAD frame enhances the probability that all the STAs 120 in
the system will utilize their scheduled ULTs, eliminating wasted
bandwidth. Essentially, the AP 110 may utilize a comparison of the
duration of individual ULTs, the total duration of all ULTs, and
the number of STAs 120 having ULTs against pre-determined
thresholds to decide whether or not a redundant MMP/PSAD frame
should be transmitted.
Referring again to FIG. 11, suppose that not only STA2 failed to
successfully receive and decode the MMP/PSAD frame, but STA3 failed
as well. In this case, both STA2 and STA3 would miss their
scheduled transmission times without remedial action by the AP 110.
Therefore, if the AP 110 were to detect an idle period for too long
after the uplink transmission (U1) of STA1, then the AP 110
transmits a redundant MMP/PSAD frame. In this way, STA3 receives
the redundant MMP/PSAD frame and transmits its data during its
scheduled uplink window (U3), thus limiting further waste of the
medium.
In yet another alternative embodiment of the present invention, the
AP 110 may schedule a broadcast or multicast frame utilizing the
MMP/PSAD frame. In order to do this, the AP 110 must reconfigure
the existing PSAD frame 40 of the MMP/PSAD frame, since the current
format specifies that the STA ID field 82 is the Association ID of
the STA 120. Therefore, to support transmitting a broadcast or
multicast frame within the MMP/PSAD sequence, the existing PSAD
frame 40 should be reconfigured.
One way to reconfigure the PSAD frame 40 is to include a bit or a
field within the MMP/PSAD frame. In a preferred embodiment, this is
included in the Station Info field. For example, a bit may be
included in the Reserved field 81 of the Station Info field,
specifying that a broadcast frame will be transmitted at specified
DLT parameters, and that STAs should remain awake during that
duration. Alternatively, specific values for the STA ID field 82,
for example all "1's", may be utilized to indicate that a broadcast
frame will be transmitted and that STAs should remain awake during
the duration. That is, the STA ID field 82 should have all bits set
to "1".
FIG. 13 is an exemplary signal diagram 131 of a downlink and uplink
exchange for the wireless communication system 100, where a
broadcast or multicast MMP/PSAD is transmitted during a broadcast
phase of the downlink phase. In the present example, the AP 110
transmits the first MMP/PSAD prior to the downlink phase that
indicates to some or all STAs 120 that they should listen during a
broadcast interval that will occur at the end of the downlink
phase. At the end of the downlink phase, the AP 110 may then
transmit a frame, and preferably an additional MMP/PSAD frame to
confirm the ULT schedules. In this manner, the STAs 120 will have
received their ULT schedules twice and therefore be less likely to
miss their uplink transmission time.
Alternatively, the AP 110 may insert a second MMP/PSAD frame with
the first MMP/PSAD frame exchange sequence by including a unicast
MMP/PSAD entry in the first MMP/PSAD frame that describes the Tx
Start Offset and the Tx Duration for when the second MMP/PSAD frame
is to be transmitted. As an example, the entry may include any MAC
address of any STA 120 as a dummy receiver address. This entry may
also include inaccurate Tx Start Offset and Tx Duration
information. At the end of the downlink phase, the AP 110 may then
transmit a frame, and preferably an additional MMP/PSAD frame to
confirm the ULT schedules. In this manner, only STAs 120 that have
not successfully received and decoded the first MMP/PSAD will
remain awake, or wake up, to receive and decode the second MMP/PSAD
frame, while those stations that successfully received and decoded
the first MMP/PSAD frame will not need to wake up to receive and
decode the second MMP/PSAD frame. This is because those STAs 120
that successfully receive and decode the first MMP/PSAD frame will
know that the second MMP/PSAD frame was not meant for them.
Alternatively, no information relating to the second MMP/PSAD frame
may be transmitted in the first MMP/PSAD frame.
FIG. 14 is an exemplary signal diagram 141 of a downlink and uplink
exchange for the wireless communication system 100, where a
broadcast or multicast MMP/PSAD is transmitted between the downlink
phase and the uplink phase. In this example, the AP 110 inserts a
second MMP/PSAD frame within the first MMP/PSAD frame, but does not
include any entry in the first MMP/PSAD frame to describe the
second one. The AP 110 then transmits the second MMP/PSAD frame to
confirm the ULT schedules in an interval between the downlink phase
and the uplink phase, as shown in FIG. 14. In this scenario, only
STAs 120 that did not successfully receive and decode the first
MMP/PSAD frame will awaken to receive the second MMP/PSAD frame
since those that did successfully receive and decode the first
MMP/PSAD frame will not awaken until they need to based on their
successful decoding of the first MMP/PSAD frame.
Importantly, however, it should be noted that the AP 110 should
account for the effect of the inserted, or nested, MMP/PSAD frame
during its ULT Offset and Duration calculations. Otherwise, the AP
110 will be out of synchronization with the Offsets that the STAs
120 believe they are required to adhere to.
This nested, or redundant MMP/PSAD frame, may or may not contain
identical information to the first MMP/PSAD frame. In a preferred
embodiment, however, it will contain the ULT information for the
STAs 120, and will typically contain consistent information with
that of the first MMP/PSAD frame. That is, the second MMP/PSAD
frame should contain the same scheduling information that was
contained in the first MMP/PSAD frame.
Although in previous embodiments, the AP 110 is described as
monitoring the medium in order to determine whether or not to
reclaim it, STAs 120 may also monitor the medium in order to
further improve system performance. Typically, the STAs 120 that
receive their ULT schedule information in the MMP/PSAD frame do not
perform sensing of the medium. They simply blindly begin their
transmissions at their scheduled ULT. However, in some instances,
it may be desirable to have the STAs 120 monitor the medium instead
of, or in addition to, the AP 110. In one embodiment, a STA 120 may
monitor the medium for any idle periods. If the STA 120 detects an
idle period lasting beyond a pre-determined threshold, that STA may
then transmit its uplink transmission during the remaining ULT
duration, thereby avoiding collisions with other STAs ULTs, while
maximizing use of the medium.
Although FIG. 1 only depicts one AP 110, it is also possible for
several APs to be present in a wireless communication system. In
this case, some STAs in the wireless communication system may be
associated with one AP, while other STAs may be associated with
other APs, which could cause some difficulty. In one scenario, one
of the APs (AP1) may be associated with an Overlapping Basic
Service Set (OBSS) or a co-channel BSS to another AP (AP2). If AP1
were to transmit an MMP/PSAD frame, STAs associated with AP2 may
ignore the MMP/PSAD frame after receiving it because they will not
see in the RA field any address that would indicate to them that
the frame is intended for them, and go into a sleep state. If AP2
then transmits traffic during that time, the intended STAs will not
receive the information because they will have been asleep during
the transmission.
Accordingly, the STAs 120 receiving an MMP/PSAD frame may be
configured to read the TA field in the frame to determine if the
MMP/PSAD frame was sent from an AP with which the STA is
associated. If the STA determines that the AP address in the TA
field is the address of the AP the STA is associated with, then the
STA can decode downlink transmissions and perform uplink
transmissions in accordance with the contents of the MMP/PSAD
frame, while going into sleep mode at other times. Conversely, if
the STA determines that the AP transmitting the MMP/PSAD frame is
not the AP the STA is associated with, it may ignore the frame, but
still remain in an awake state to receive any transmission that
might be sent from its associated AR Additionally, however, the STA
may desire to read the Duration ID value in an MMP/PSAD frame and
update its NAV Duration, even if the frame was not sent by an
associated AP. In this manner, the STA will know when the medium
will be in use, and will be able to avoid transmitting during those
times.
In another alternative embodiment of the present invention, the
MMP/PSAD frame may be utilized to poll certain types of packets,
such as Block Acknowledgement (BA) response frames. In this case,
the AP 110 may utilize one or more flags within the MMP/PSAD frame
indicating to specified STAs 120 that they transmit their BA
response frames during their scheduled ULTs. The flag may further
indicate to the STAs 120 whether or not they are to transmit only
BA response frames during their scheduled ULT, or if they are to
transmit BA response frames along with other frames the STA is
transmitting. This alternative facilitates the addition of a new
mode for BA to the currently existing modes.
Currently, the existing BA modes include Immediate Block ACK and
Delayed Block ACK. In Immediate Block ACK mode, a STA responds to a
BA request (BAR) immediately following an SIFS delay. In Delayed
Block ACK mode, a STA decides on its own when to transmit a BA
frame.
The present alternative embodiment includes polling for a Delayed
BA, as opposed to the BA being transmitted at an arbitrary time by
the STA. For example, the AP 110 may transmit a BAR to the STA 120
indicating to the STA 120 that the STA 120 should prepare the BA
packet, or BA frame, and only transmit the packet when the STA 120
receives another poll message from the AP 110. The poll message may
be in the form of an MMP or another packet transmitted by the AP
110. This provides for the AP 110 to determine the time for
associated STAs 120 to transmit their BA frames instead of having
the STAs themselves determine when to transmit them.
The above features may be implemented in a wireless
transmit/receive unit (WTRU), base station, and/or peer-to-peer
devices. The above methods are applicable to a physical layer
and/or a data link layer. The applicable forms of implementation
include application specific integrated circuit (ASIC), middleware,
and software. This invention can be applied in an OFDM/MIMO system
and a IEEE 802.11 compliant system.
Additionally, the features of the embodiments of the present
invention may be implemented in a variety of manners, such as in an
application running on a WTRU, such as an AP or STA. The features
may also be incorporated into an integrated circuit (IC) or be
configured in a circuit comprising a multitude of interconnecting
components. Additionally, the features may be performed by a
software application that runs on an IC, or by a software
application that runs on a processor.
Although the features and elements of the present invention are
described in the preferred embodiments in particular combinations,
each feature or element can be used alone (without the other
features and elements of the preferred embodiments) or in various
combinations with or without other features and elements of the
present invention.
* * * * *